The modern shipbuilding industry requires a very high-quality steel capable of performing reliably under harsh conditions. The steel must be strong enough to withstand unpredictable weather, heavy loads, and extended periods of use. The steel must retain its toughness even at low temperatures and must be weldable over a wide range of temperatures without pre-heating so that repairs and modifications can be made quickly and safely at sea. Finally, the relationship of strength to weight must be high in order to increase manueverability and decrease valuable fuel consumption.
The demands of shipbuilding for military use are even more rigorous. The steel must meet all the criteria discussed above, plus it must perform completely reliably under battle conditions. The United States Department of the Navy has specified properties which must be present in steels used in combatant ship hulls. These steels are known as Grade HY-80 and HY-100 steels.
Currently, the steels which satisfy the HY-80 and Hy-100 specifications are rolled, as well as cast, steels, primarily those strengthened by precipitation-hardening. However, stronger rolled steels often require new tooling for their fabrication due to their greater resistance to deformation and elongation. In addition, these steels are not easily weldable in harsh or emergency conditions due to their need for pre- and/or post-heat treatments.
Accordingly, there exists a need for a steel which meets the criteria for military shipbuilding, which is easily cast or shaped, and which is weldable even at low temperatures, and in the demanding conditions present at sea and in battle.